Buddha said the following
There is the case where a certain excellent thoroughbred person hears, ‘In that town or village over there a man or woman is in pain or has died.’ He is stirred & agitated by that. Stirred, he becomes appropriately resolute. Resolute, he both realizes with his body the highest truth and, having penetrated it with discernment, sees. This type of excellent thoroughbred person, I tell you, is like the excellent thoroughbred horse who, on seeing the shadow of the goad-stick, is stirred & agitated. Some excellent thoroughbred people are like this. And this is the first type of excellent thoroughbred person to be found existing in the world." -Buddha
Here he mentioned something different. But I quoted because I believe mindfulness of death and mindfulness of body has the same recollection that the same will happen to you.
He taught mindfulness of death body before mindfulness of breathing. So I think he started to teach that first. So I think since it’s the best taught by him. In modern times, since practicing is difficult, we have to directly go for the best.
We should atleast try